The present invention relates to a knocking control system for preventing knocking of an automotive engine which is provided with a fail-safe system, and more particularly to a system capable of preventing damage due to high exhaust gas temperature which is caused by keeping the ignition timing retardation at a full extent by the function of fail-safe system in case of malfunction of a knock sensor.
Knock control systems are usually mounted within an ignition timing control system with a distributor and have the function of electrically processing a signal from the knock sensor to detect the occurrence of knocking. When the system determines that knocking of the engine occurs, it acts to retard the ignition timing to a maximum extent so that knocking does not occur.
Japanese Patent Laid-Open No. 56-47663 disclosed a fail-safe system which operates to hold the ignition timing to the maximum retard when a knock sensor malfunctions because of reasons such as: faulty contacts of connectors; electrical release; short circuit, etc.
However, if the engine operates at an extremely retarded ignition timing, the amount of CO in the exhaust gases increases due to incomplete combustion. A large amount of CO is treated by oxidation in an exhaust gas purification system mounted on the vehicle, resulting in elevation of the exhaust gas temperature which causes damage in the exhaust system.